Term
| what portion of total digestion is the small intestine responsible for? |
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Definition
| 90% -esp lipid digestion, which occurs in the first 2 segments |
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Term
| what is the only essential segment of the gut? |
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Definition
| the small intestine - resection is fatal |
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Term
| how long does chyme take to go through the small intestine? |
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Definition
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Term
| what portion of dietary nutrients (water, electrolytes) are approx absorbed in the *small intestine* (not large)? why? |
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Definition
| almost all dietary nutrients (including *water and electrolytes) are absorbed in the small intestine because chyme there is isosmotic (otherwise it would change the somolarity of the extracellular fluid). therefore, what is left behind is still isosmotic and the water left over in that is absorbed in the large intestine |
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Term
| what contributes to the large amount of surface area in the small intestine? |
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Definition
| epithelial folds, villi, microvilli - the small intestine is approx the surface area of a football field if totally laid out |
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Term
| why is simply the fact that the sm intestine has a large surface area not enough for good absorption to take place? |
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Definition
| the food has to be moved, mixed and pressed against the intestinal walls (embedded with peptidases, maltases, etc) in order to be absorbed fully |
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Term
| what characterizes the segmental non-propulsive motor activity of the small intestine? |
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Definition
| there are segmental contractions that mix the food with no net forward movement |
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Term
| what is the general fashion in which peristalsis occurs in the small intestine? |
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Definition
| there is relaxation before the chyme and contraction behind it |
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Term
| what characterizes the housekeeping waves in the small intestine? |
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Definition
| the housekeeping waves or "migrating motor complexes" occur once everything that needs to be absorbed is absorbed and the remaining chyme is moved out |
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Term
| what does the efficiency of absorption in the small intestine depend on? |
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Definition
| adequate form of absorption (digestion must be adequate), adequate surface for absorption (large margin of safety - 50% of the sm intestine is safely removable), adequate rate of transit through the intestine (duodenum coordinates speed of stomach emptying/bile secretion, jejunum - absorption of B12, ileum - absorbs/recirculates bile salts) and specific co-factors/carriers being available |
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Term
| what are the effects of aging on the sm intestine? what is the net effect? |
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Definition
| the villia shrink and broaden w/age, less enzymes are produced, and epithelial stem cell division slows - leaving the digestive epithelium more susceptible to damage. the net effect is *decreased efficiency in absorbing nutrients/vitamins |
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Term
| how are carbs digested in the sm intestine? |
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Definition
| before even reaching the stomach, carbs are partially digested in the mouth by salivary amylase and completely digested in the sm intestine via pancreatic amylase |
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Term
| where does protein digestion start? where do protein fragments go? |
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Definition
| in the stomach via pepsin which is continued in the small intestine via trypsin/chymotrypsin and pepdidase in the jejunum. protein fragments are carried via amino acid cotransporters into the hepatic portal vein and then all go to the liver |
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Term
| how is fat digested generally? |
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Definition
| fat is broken down to glycerol/fatty acids in the stomach via lipase, then broken down further to mono/trigylcerides. fat is completely broken down in the sm intestine unlike carbs/proteins and is emulsified by bile from the liver (chylomicrons are released into lymph) |
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Term
| what vessels are lipids (which have been digested and absorbed) carried through? |
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Definition
| the thoracic duct (from the intestinal lymphatics) |
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Term
| what is the cobalamin complex (intrinstic factor) very resistant to? |
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Definition
| pancreatic digestive enzymes |
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Term
| where in the small intestine are vitamins absorbed? |
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Definition
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Term
| how are the fat soluble vitamins absorbed? |
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Definition
| along with the fat - they are eventually taken to the liver |
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Term
| which vitamins are water soluble? how long due they remain in the body? |
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Definition
| the B and C vitamins, which get flushed out of the body fairly quickly |
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Term
| why is more water absorbed in the small intestine? |
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Definition
| because water is osmotically obligated to follow the nutrients, of which the majority are absorbed in the small intestine. (H2O always follows passively down a concentration gradient in order to keep the nutrients isosmotic as they are being absorbed) |
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Term
| what is the primary job of the large intestine? |
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Definition
| to absorb water left in the feces (if LI did not absorb water - we would have too loose stools) |
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Term
| is the ileocecal valve a sphincter? |
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Definition
| no, just smooth muscle wrapped around the tube (a thickening of the muscular wall) |
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Term
| what is the function of the ileocecal valve? |
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Definition
| allowing small amounts of chyme into the cecum (first part of the large intestine), after which it closes to prevent retrograde flow of material. |
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Term
| how is the ileocecal valve controlled? |
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Definition
| the ileocecal valve is opened by the long arc vagal reflex, which is initiated by food entering the stomach, as well as gastrin release (the ileocecal valve has gastrin receptors), which controls how long it stays open. (irritation and pressure can also relax the valve and excite peristalsis via the myenteric plexus) |
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Term
| what is the cecoileal reflex? |
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Definition
| material collects in the cecum (area proximal to the valve) and impinges on the valve, which stimulates a vagally mediated reflex by inhibitor neurons. therefore it is a partially physiologic reflex. |
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Term
| other than with the cecoileal reflex, where else in the body can a physiologic sphincter be found? |
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Definition
| the stomach is arranged in a J-shape, allowing food to bulge back and close the lower valve of the LES. (the smooth muscle is a little weak and this is an adaptation that takes place to reinforce it) |
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Term
| can the cecoileal valve fail? |
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Definition
| yes, its not unusual to have fecal contents exit the mouth. this demands immediate medical intervention. |
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Term
| what is the ileal break reflex? |
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Definition
| incomplete digestive processes slow down emptying (vagal reflex) |
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Term
| what is the intestino-intestinal reflex? |
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Definition
| blockage or distention inhibits motility overall (sympathetics - local through the myenteric plexus) |
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Term
| what is ileogastric distention reflex? |
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Definition
| this decreases gastric motility (vagal reflex) |
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Term
| what is the postop ileus reflex? |
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Definition
| ileus is a very common occurrence w/abdominal sx in which the bowels become atonic due to handling of smooth muscle. it is a physiologic reflex. |
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Term
| what is the gastrocolic reflex? |
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Definition
| when the stomach fills, a strong peristaltic wave moves contents of the transverse colon into the rectum (common in babies and adults after morning coffee) |
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Term
| what is the gastroilieal reflex? |
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Definition
| increased terminal ileal motility and emptying into the colon |
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Term
| what is obstruction pathophysiology dependent upon? |
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Definition
| degree of obstruction, duration of obstruction, and *presence/severity of ischemia. |
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Term
| what does obstruction pathophysiology result in? |
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Definition
| accumulation of fluid/air, bacterial overgrowth, max 24 hrs after obstruction, ischemia and gut translocation to nodes/portal system |
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Term
| once the gut is distended due to obstruction, what can you get? |
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Definition
| impaired fluid and nutrient absorption, secretion of isotonic fluid (intravascular -> intraluminal) thought secondary to bacterial overgrowth |
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Term
| what is treatment for obstruction? |
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Definition
| OMT, gas inhalation - give pt 100% O2 to breathe and dilute partial pressure of N in blood stream, then N will diffuse down its concentration gradient from gut into bloodstream and get blown off by lungs |
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